Electronic device

ABSTRACT

An electronic device of a novel embodiment, specifically an arm-worn electronic device used while being worn on an arm, is provided. An arm-worn secondary battery used while being worn on an arm is provided. An electronic device is provided, which includes a structure body having a curved surface as a support structure body, a flexible secondary battery including a film as an exterior body over the curved surface of the support structure body, and a display portion including a plurality of display elements between a pair of films over the secondary battery. The plurality of display elements and the secondary battery overlap with each other at least partly. It is possible to provide an electronic device which has a small maximum thickness of 1 cm or less and a light weight of 50 g or less even when an arm-worn secondary battery is provided with a display portion.

TECHNICAL FIELD

The present invention relates to electronic devices.

Note that electronic devices in this specification generally meandevices including secondary batteries, and electro-optical devicesincluding secondary batteries, information terminal devices includingsecondary batteries, and the like are all electronic devices.

BACKGROUND ART

Display devices used while being worn on human bodies, such as displaydevices mounted on heads, have recently been developed and are referredto as head-mounted displays or wearable displays. It is desired that notonly display devices but also electronic devices used while being wornon human bodies, such as hearing aids, have a light weight and a smallsize.

Along with a decrease in weight of electronic devices, it is demandedthat batteries for supplying power to electronic devices also have alight weight and a small size.

Electronic books including flexible display devices are disclosed inPatent Documents 1 and 2.

PATENT DOCUMENTS

-   [Patent Document 1] Japanese Published Patent Application No.    2010-282181-   [Patent Document 2] Japanese Published Patent Application No.    2010-282183

DISCLOSURE OF INVENTION

In order that a user can comfortably wear a display device used whilebeing worn on a human body, the display device needs to have a lightweight and a small size, and in addition, the whole electronic deviceincluding a driver device for the display device and a power sourceneeds to have a light weight.

An electronic device of a novel embodiment, specifically, an arm-wornelectronic device used while being worn on an arm, is provided. Anarm-worn secondary battery used while being worn on an arm is provided.

An arm-worn secondary battery is obtained, in which a structure bodyhaving a curved surface to be in contact with part of a human body isused as a support structure body and a flexible secondary battery isfixed to the support structure body along the curved surface. It ispreferable that the secondary battery be thin so that the secondarybattery is flexible, and specifically, it is preferable to use asecondary battery with an increased volume energy density and a smallnumber of electrode layers. The term “a small number of electrodelayers” means a small number of stacked electrode pairs each including apositive electrode and a negative electrode, or a small number ofwindings in a wound battery. It is preferable that the arm-wornsecondary battery have a small maximum thickness of 1 cm or less.

An embodiment of a band-like secondary battery to be worn on an arm isgiven as an example. In this embodiment, the secondary battery providedover the support structure body has an arch-like cross-sectional shape.In wearing the secondary battery, an end portion of the supportstructure body bends; thus, an end portion of the secondary battery alsobends. Although the end portion of the secondary battery bends, sincethe secondary battery has flexibility, an exterior body of the secondarybattery is not damaged and the secondary battery can retain batteryperformance.

A structure disclosed in this specification is an electronic devicewhich includes a structure body having a curved surface and a flexiblesecondary battery being in contact with at least part of the curvedsurface of the structure body and including a film as an exterior body,and which is worn such that the curved surface of the structure body isin contact with a user's arm.

The flexible secondary battery includes the film as the exterior bodyand can change its shape along a curved surface portion of the structurebody. In a region surrounded by the exterior body, a positive electrode,a negative electrode, and an electrolytic solution are provided. It isparticularly preferable to use, as the secondary battery, a lithium-ionsecondary battery which achieves a high energy density and therefore hasa light weight and a small size.

In the above structure, the structure body is to be in contact with anarm and the flexible secondary battery is provided over the structurebody. However, the present invention is not particularly limited to thisexample, and the flexible secondary battery may be provided between thestructure body and the arm. A structure in that case is an electronicdevice which includes a structure body having a curved surface and aflexible secondary battery being in contact with at least part of thecurved surface of the structure body and including a film as an exteriorbody, and which is worn such that the film is in contact with a user'sarm.

In the above structure, a display portion may also be provided. Astructure in that case is an electronic device which includes astructure body having a curved surface, a flexible secondary batteryincluding a film as an exterior body over the curved surface of thestructure body, and a display portion including a plurality of displayelements between a pair of films over the secondary battery. Theplurality of display elements and the secondary battery overlap witheach other at least partly.

The larger the area where the plurality of display elements and thesecondary battery overlap with each other is, the warmer the secondarybattery can be made by use of heat generated by the display elements.Lithium-ion secondary batteries result in particularly poor performanceat low temperatures in cold climates; thus, it is important to warm thesecondary battery. Since the electronic device is worn on an arm and thesecondary battery is located between the arm and the display elements,the secondary battery can be warmed efficiently from both front and backsurface sides of the secondary battery. Furthermore, a highly heatconductive material may be used as a material of the structure body toeffectively warm the secondary battery.

Alternatively, the secondary battery may be in contact with an arm, anda structure in that case is an electronic device which includes astructure body having a curved surface and a flexible secondary batterybeing in contact with at least part of the curved surface of thestructure body and including a film as an exterior body, and which isworn such that the film is in contact with a user's arm. By contact withthe user's arm, the secondary battery can be warmed.

In each of the above structures, one of the pair of films, between whichthe display portion including the plurality of display elements islocated, on the side closer to the structure body may be a metal filmsuch as a stainless steel film.

In each of the above structures, the display portion is preferably anactive-matrix display device in which a plurality of display elementsare arranged in a matrix. As the display elements, organiclight-emitting elements, electronic ink, or the like can be used, andorganic light-emitting elements are particularly preferable because theyare as thin as, or thinner than, 3 mm and are lightweight.

When the display portion of the arm-worn electronic device is usedtogether with a display portion of a conventional portable informationterminal, the display portion of the arm-worn electronic device may beused as a sub-display.

In addition to the display device, each of the above structures mayinclude another semiconductor circuit, e.g., a control circuit forpreventing overcharge, an imaging element, a sensor such as a gyroscopesensor or an acceleration sensor, a touch panel, or the like. Forexample, when an imaging element is included in addition to the displaydevice, a taken image can be displayed on the display device. When asensor such as a gyroscope sensor or an acceleration sensor is included,the arm-worn electronic device can be powered on or off depending on theorientation or movement thereof to reduce power consumption. When atouch panel is included, the electronic device can be operated orinformation can be input by touching a predetermined position of thetouch panel. When a memory and a CPU are included in addition to thedisplay device in the above structure, a wearable computer can beobtained.

Furthermore, an antenna may be provided, and a structure in that case isan electronic device which includes a structure body having a curvedsurface, a flexible secondary battery being in contact with at leastpart of the curved surface of the structure body and including a film asan exterior body, and an antenna electrically connected to the secondarybattery, and which is worn such that the curved surface of the structurebody is in contact with a user's arm.

With the antenna, the secondary battery can be charged without contact.By an electromagnetic induction method in which an antenna of a charger(primary coil) and the antenna of the electronic device (secondary coil)are magnetically coupled and a voltage is generated at the secondarycoil with an alternating magnetic field generated from the primary coil,electric power is transmitted to the secondary coil side withoutcontact. Through this mechanism, the secondary battery is charged. It ispreferable that the antenna be provided in contact with the curvedsurface of the structure body; therefore, it is preferable that theantenna of the electronic device be provided over a flexible film.

The arm-worn secondary battery may be provided with an antenna forpurposes other than contactless charging of the secondary battery. Amemory may be further provided, and an antenna that enables electronicdata transmission and reception or an antenna that enables display ofposition or time with a GPS function by obtaining positional informationor GPS time may be provided.

An antenna and a transmission and reception circuit for use as an activetag may be provided so that the arm-worn secondary battery can functionas an active tag. The term “active tag” means a wireless IC tag (RFID)that includes a battery and can conduct communication.

The arm-worn secondary battery can function as a spare secondary batteryfor supplying power to a portable information terminal. A portableinformation terminal such as a smartphone is carried around withoutbeing powered off to stand by for an incoming email or call. As timeelapses, the amount of remaining battery power decreases, and theportable information terminal runs out of power. When the portableinformation terminal has various functions such as a camera and asensor, it is difficult to decrease its weight, and the space for thesecondary battery is small. Even when the performance of the secondarybattery included in the portable information terminal is improved,secondary batteries inevitably deteriorate by repeated use, and thesecondary battery with improved performance is very expensive.

It is needless to say that a secondary battery of the same kind as thatincluded in the portable information terminal may be purchased as aspare secondary battery and may be carried around all the time. However,in terms of safety, many portable information terminals are designedsuch that secondary batteries cannot be freely replaced by users. Acharging module used as a spare secondary battery for charging aportable information terminal is also commercially available; however,the charging module is as large as or larger than the portableinformation terminal, and is heavier than the portable informationterminal and specifically weighs 150 g or more. A spare secondarybattery needs to be carried in a user's pocket or bag all the time, andis difficult to carry when a user wears clothes without pockets or whena user cannot carry a bag.

When a user also has an arm-worn secondary battery used while being wornon an arm, this can be used as an auxiliary power source after thesecondary battery of the portable information terminal runs out ofpower. When a user wears it on his/her arm, it is not necessary to carrya spare secondary battery in his/her pocket or bag, which is convenient.The arm-worn secondary battery worn on an arm has an attractive design.Since the display portion and the secondary battery overlap with eachother, when an image is displayed on the display portion, the secondarybattery is hidden or camouflaged. Thus, other people recognize theelectronic device worn on an arm as an accessory, not a spare secondarybattery, and do not feel strange. This is particularly favorable forwomen because women often wear clothes without pockets and they careabout how they look.

When the arm-worn secondary battery includes a display portion capableof displaying full-color images, the arm-worn secondary battery can bereferred to as an arm-worn digital photo frame. A user can choosefavorite images (pictures etc.) to be displayed on the arm-wornsecondary battery.

The arm-worn secondary battery used while being worn on an arm islightweight and weighs less than 150 g, preferably 100 g or less, morepreferably 50 g or less as a whole, depending on the capacity of thesecondary battery. When the arm-worn secondary battery is used as anauxiliary power source, the power does not always need to be on. Bykeeping the power off, a decrease in remaining battery power can besuppressed.

When the secondary battery is intended to be mainly used as a sparesecondary battery, the display portion does not need to be capable ofdisplaying full-color images and may be capable of displaying monochromeor mono-color images and may be capable of displaying only the amount ofremaining battery power.

In each of the above structures, a metal or a resin can be used for thesupport structure body. Alternatively, a metal may be mainly used and aresin may be partly used for the support structure body, or a resin maybe mainly used and a metal may be partly used for the support structurebody. As the metal, stainless steel, aluminum, a titanium alloy, or thelike can be used. As the resin, an acrylic resin, a polyimide resin, orthe like can be used. A natural material can be used as a material ofthe support structure body, and as the natural material, processed wood,stone, bone, leather, paper, or cloth can be used.

It is possible to provide an electronic device which has a small maximumthickness of 1 cm or less and a light weight of 50 g or less even whenan arm-worn secondary battery is provided with a display portion. It ispossible to provide an electronic device which can be worn on an arm andis suitable for being carried around without being held with eitherhand. The arm-worn secondary battery can display an image on its displayportion and can also be used as an accessory.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are a cross-sectional view and a perspective viewillustrating one embodiment of the present invention.

FIGS. 2A and 2B are a top view and a cross-sectional view illustratingone embodiment of the present invention.

FIG. 3 is a perspective view illustrating one embodiment of the presentinvention.

FIGS. 4A and 4B are cross-sectional views illustrating one embodiment ofthe present invention.

FIG. 5 is a photograph showing one embodiment of the present invention.

FIG. 6 is a cross-sectional view illustrating one embodiment of thepresent invention.

FIGS. 7A to 7C are a cross-sectional view, a bottom view, and a sideview illustrating one embodiment of the present invention.

FIGS. 8A to 8C illustrate a center of curvature.

FIGS. 9A to 9C illustrate a radius of curvature of a surface.

FIGS. 10A to 10F are perspective views and cross-sectional viewsillustrating one embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to drawings. However, the present invention is notlimited to the description below, and it is easily understood by thoseskilled in the art that modes and details disclosed herein can bemodified in various ways. Further, the present invention is notconstrued as being limited to description of the embodiments.

Embodiment 1

In this embodiment, an example of an electronic device in which anarm-worn secondary battery is provided with a display portion isdescribed. FIG. 1A is a cross-sectional view of the electronic device,and FIG. 1B is a perspective view of the electronic device.

As illustrated in FIG. 1A, an electronic device 100 includes a flexiblesecondary battery 103 over a curved surface of a support structure body101 and a display portion 102 over the secondary battery 103.

The support structure body 101 is in the form of a bracelet obtained bycurving a band-like structure body. At least part of the supportstructure body 101 has flexibility and can be moved in the direction ofarrows 105; thus, the electronic device can be put around a wrist. Anend portion of the support structure body 101 illustrated in FIG. 1A isbendable, and a middle portion apart from the end portion hardly changesits shape. Therefore, the middle portion of the support structure body101 maintains a curvature with which the secondary battery and thedisplay portion are attached and fixed in fabrication; thus, thesecondary battery 103 and the display portion 102 overlapping with themiddle portion are hardly damaged even when the electronic device isrepeatedly put on and taken off from an arm.

In the case where an active-matrix display device is provided as thedisplay portion, the active-matrix display device includes at least alayer including transistors. The reliability of the layer includingtransistors is not easily decreased when the layer is only attached toand fixed to the curved surface of the support structure body 101.However, the reliability might be decreased when the layer includingtransistors is repeatedly bent in such a manner that the layer includingtransistors is curved toward one side into a concave shape, returned toa flat shape, and then curved toward the other side into a convex shape.Also in this regard, since the middle portion of the support structurebody 101 illustrated in FIG. 1A hardly changes its shape, when the layerincluding transistors is fixed to the curved surface of the supportstructure body 101, the layer is curved toward only one side even if itis bent. In other words, the support structure body 101 functions as aprotective member which prevents the display portion 102 and thesecondary battery 103 from being curved excessively or from beingtwisted and deformed significantly.

As a material of the support structure body 101, a metal, a resin, anatural material, or the like can be used. The support structure body101 preferably has a small thickness so as to be lightweight. A metal ispreferably used as a material of the support structure body 101 becausea metal has high impact resistance and high heat conductivity. A resinis preferably used as a material of the support structure body 101because the resin can achieve a reduction in weight and does not causemetal allergy.

The shape of the electronic device illustrated in FIG. 1B is an example,and a belt or a clasp for fixing to a wrist may be provided.Alternatively, the electronic device may be in the form of a ring or acylinder tube so as to surround a wrist.

Although the example of the electronic device to be worn on an arm suchas a wrist (a lower arm including a wrist) or an upper arm is described,the position is not particularly limited, and the electronic device maybe worn on any part of a human body such as a waist or an ankle. In thecase where the electronic device is worn on an ankle, the electronicdevice may be manufactured to have a shape different from thatillustrated in FIGS. 1A and 1B and have a size to fit an ankle shape. Inthe case where the electronic device is worn on a waist, the electronicdevice may be manufactured in a size to be wrapped around a waist like abelt.

An example of a method for manufacturing the electronic device 100 isdescribed below.

First, the support structure body 101 is prepared. A stainless steelmaterial whose region with a large radius of curvature in across-section does not change its shape and whose end portion isbendable is used for the support structure body 101. The stainless steelmaterial serves as a protective material which prevents the displayportion 102 and the secondary battery 103 from being curved excessivelyor from being twisted and deformed significantly. The stainless steelmaterial only allows a change into a certain shape, i.e., bending in onedirection, in putting the electronic device on an arm, which improvesthe reliability.

Next, the secondary battery 103 to be attached to the region with alarge radius of curvature of the support structure body 101 is prepared.

The secondary battery 103 is not particularly limited as long as it is alithium-ion secondary battery and is flexible. The flexible secondarybattery includes a thin flexible film as an exterior body and can changeits shape along a curved surface portion of the region with a largeradius of curvature of the support structure body 101.

In this embodiment, an example in which a laminated secondary battery isused as the flexible secondary battery is described. FIG. 2A illustratesa top view of the laminated secondary battery. FIG. 2B is a schematiccross-sectional view taken along a dashed-dotted line A-B in FIG. 2A.

A secondary battery used is fabricated in such a manner that asheet-like positive electrode 203, a separator 207, and a sheet-likenegative electrode 206 are stacked, the other region is filled with anelectrolytic solution 210, and these components arc enclosed by anexterior body made of one or two films. Note that the positive electrode203 includes a positive electrode current collector 201 and a positiveelectrode active material layer 202. The negative electrode 206 includesa negative electrode current collector 204 and a negative electrodeactive material layer 205.

The positive electrode current collector 201 and the negative electrodecurrent collector 204 can each be formed using a highly conductivematerial which is not alloyed with a carrier ion of lithium or the like,such as a metal typified by stainless steel, gold, platinum, zinc, iron,nickel, copper, aluminum, titanium, or tantalum or an alloy thereof.Alternatively, an aluminum alloy to which an element which improves heatresistance, such as silicon, titanium, neodymium, scandium, ormolybdenum, is added can be used. Still alternatively, a metal elementwhich forms silicide by reacting with silicon can be used. Examples ofthe metal element which forms silicide by reacting with silicon includezirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium,molybdenum, tungsten, cobalt, nickel, and the like. The positiveelectrode current collector 201 and the negative electrode currentcollector 204 can each have a foil-like shape, a plate-like shape(sheet-like shape), a net-like shape, a cylindrical shape, a coil shape,a punching-metal shape, an expanded-metal shape, or the like asappropriate. The positive electrode current collector 201 and thenegative electrode current collector 204 each preferably have athickness greater than or equal to 10 μm and less than or equal to 30μm.

For the positive electrode active material layer 202, a material intoand from which lithium ions can be inserted and extracted can be used.For example, a lithium-containing material with an olivine crystalstructure, a layered rock-salt crystal structure, and a spinel crystalstructure can be used. As the positive electrode active material, acompound such as LiFeO₂, LiCoO₂, LiNiO₂, LiMn₂O₄, V₂O₅, Cr₂O₅, and MnO₂can be used.

Typical examples of the lithium-containing material with an olivinecrystal structure (represented by a general formula, LiMPO₄ (M is one ormore of Fe(II), Mn(II), Co(II), and Ni(II)), are LiFePO₄, LiNiPO₄,LiCoPO₄, LiMnPO₄, LiFe_(a)Ni_(b)PO₄, LiFe_(a)Co_(b)PO₄,LiFe_(a)Mn_(b)PO₄, LiNi_(a)Co_(b)PO₄, LiNi_(a)Mn_(b)PO₄ (a+b≤1, 0<a<1,and 0<b<1), LiFe_(c)Ni_(d)Co_(e)PO₄, LiFe_(c)Ni_(d)Mn_(e)PO₄,LiNi_(c)Co_(d)Mn_(e)PO₄ (c+d+e≤1, 0<c<1, 0<d<1, and 0<e<1), andLiFe_(f)Ni_(g)Co_(h)Mn_(i)PO₄ (f+g+h+i≤1, 0<f<1, 0<g<1, 0<h<1, and0<i<1).

LiFePO₄ is particularly preferable because it properly has propertiesnecessary for the positive electrode active material, such as safety,stability, high capacity density, high potential, and the existence oflithium ions which can be extracted in initial oxidation (charging).

Examples of the lithium-containing material with a layered rock-saltcrystal structure include lithium cobalt oxide (LiCoO₂); LiNiO₂; LiMnO₂;Li₂MnO₃; an NiCo-based lithium-containing material (a general formulathereof is LiNi_(x)Co_(1−x)O₂ (0<x<1)) such as or LiNi_(0.8)Co_(0.2)O₂;an NiMn-based lithium-containing material (a general formula thereof isLiNi_(x)Mn_(1−x)O₂ (0<x<1)) such as LiNi_(0.5)Mn_(0.5)O₂; and anNiMnCo-based lithium-containing material (also referred to as NMC, and ageneral formula thereof is LiNi_(x)Mn_(y)Co_(1−x−y)O₂ (x>0, y>0, x+y<1))such as LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂. Moreover, the examples furtherinclude Li(Ni_(0.8)Co_(0.15)Al_(0.05))O₂ and Li₂MnO₃—LiMO₂ (M=Co, Ni, orMn).

Examples of the lithium-containing material with a spinel crystalstructure include LiMn₂O₄, Li_(1+x)Mn_(2−x)O₄, Li(MnAl)₂O₄, andLiMn_(1.5)Ni_(0.5)O₄.

It is preferable to add a small amount of lithium nickel oxide (LiNiO₂or LiNi_(1−x)MO₂ (M=Co or Al, for example)) to a lithium-containingmaterial with a spinel crystal structure which contains manganese suchas LiMn₂O₄ because advantages such as minimization of the elution ofmanganese and the decomposition of an electrolytic solution can beobtained.

Alternatively, a lithium-containing material represented by a generalformula, Li_((2−j))MSiO₄ (M is one or more of Fe(II), Mn(II), Co(II),and Ni(II), 0≤j≤2), can be used as the positive electrode activematerial. Typical examples of Li_((2−j))MSiO₄ (general formula) includelithium compounds such as Li_((2−j))FeSiO₄, Li_((2−j))NiSiO₄,Li_((2−j))CoSiO₄, Li_((2−j))MnSiO₄, Li_((2−j))Fe_(k)Ni_(l)SiO₄,Li_((2−j))Fe_(k)Co_(l)SiO₄, Li_((2−j))Fe_(k)Mn_(l)SiO₄,Li_((2−j))Ni_(k)Co_(l)SiO₄, Li_((2−j))Ni_(k)Mn_(l)SiO₄ (k+l≤1, 0<k<1,and 0<l<1), Li_((2−j))Fe_(m)Ni_(n)Co_(q)SiO₄,Li_((2−j))Fe_(m)Ni_(n)Mn_(q)SiO₄, Li_((2−j))Ni_(m)Co_(n)Mn_(q)SiO₄(m+n+q≤1, 0<m<1, 0<n<1, and 0<q<1), andLi_((2−j))Fe_(r)Ni_(s)Co_(t)Mn_(u)SiO₄ (r+s+t+u≤1, 0<r<1, 0<s<1, 0<t<1,and 0<u<1).

Still alternatively, a NASICON compound represented by a generalformula, A_(x)M₂(XO₄)₃ (A=Li, Na, or Mg, M=Fe, Mn, Ti, V, Nb, or Al, andX=S, P, Mo, W, As, or Si), can be used as the positive electrode activematerial. Examples of the NASICON compound include Fe₂(MnO₄)₃,Fe₂(SO₄)₃, and Li₃Fe₂(PO₄)₃. Still further alternatively, a compoundrepresented by a general formula, Li₂MPO₄F, Li₂MP₂O₇, or Li₅MO₄ (M=Fe orMn), a perovskite fluoride such as NaF₃ or FeF₃, a metal chalcogenide (asulfide, a selenide, or a telluride) such as TiS₂ or MoS₂, alithium-containing material with an inverse spinel crystal structuresuch as LiMVO₄, a vanadium oxide-based (e.g., V₂O₅, V₆O₁₃, or LiV₃O₈), amanganese oxide-based, or an organic sulfur-based material can be usedas the positive electrode active material, for example.

The positive electrode active material layer 202 may further include abinder for increasing adhesion of active materials, a conductiveadditive for increasing the conductivity of the positive electrodeactive material layer 202, and the like in addition to theabove-described positive electrode active materials.

A material with which lithium can be dissolved and precipitated or amaterial into and from which lithium ions can be inserted and extractedcan be used for the negative electrode active material layer 205; forexample, a lithium metal, a carbon-based material, or an alloy-basedmaterial can be used.

The lithium metal is preferable because of its low redox potential(3.045 V lower than that of a standard hydrogen electrode) and highspecific capacity per unit weight and per unit volume (3860 mAh/g and2062 mAh/cm³).

Examples of the carbon-based material include graphite, graphitizingcarbon (soft carbon), non-graphitizing carbon (hard carbon), a carbonnanotube, graphene, carbon black, and the like.

Examples of the graphite include artificial graphite such as meso-carbonmicrobeads (MCMB), coke-based artificial graphite, or pitch-basedartificial graphite and natural graphite such as spherical naturalgraphite.

Graphite has a low potential substantially equal to that of a lithiummetal (0.1 V to 0.3 V vs. Li/Li⁺) when lithium ions are intercalatedinto the graphite (while a lithium-graphite intercalation compound isformed). For this reason, a lithium-ion secondary battery can have ahigh operating voltage. In addition, graphite is preferable because ofits advantages such as relatively high capacity per unit volume, smallvolume expansion, low cost, and safety greater than that of a lithiummetal.

For the negative electrode active material, an alloy-based materialwhich enables charge-discharge reactions by an alloying reaction and adealloying reaction with lithium can be used. In the case where carrierions are lithium ions, a material containing at least one of Mg, Ca, Al,Si, Ge, Sn, Pb, Sb, Bi, Ag, Au, Zn, Cd, In, Ga, and the like can be usedas an alloy-based material, for example. Such elements have highercapacity than carbon. In particular, silicon has a significantly hightheoretical capacity of 4200 mAh/g. For this reason, silicon ispreferably used for the negative electrode active material. Examples ofthe alloy-based material using such elements include SiO, Mg₂Si, Mg₂Ge,SnO, SnO₂, Mg₂Sn, SnS₂, V₂Sn₃, FeSn₂, CoSn₂, Ni₃Sn₂, Cu₆Sn₅, Ag₃Sn,Ag₃Sb, Ni₂MnSb, CeSb₃, LaSn₃, La₃Co₂Sn₇, CoSb₃, InSb, SbSn, and thelike. Note that SiO refers to the powder of a silicon oxide including asilicon-rich portion and can also be referred to as SiO_(y) (2>y>0).Examples of SiO include a material containing one or more of Si₂O₃,Si₃O₄, and Si₂O and a mixture of Si powder and silicon dioxide (SiO₂).Furthermore, SiO may contain another element (e.g., carbon, nitrogen,iron, aluminum, copper, titanium, calcium, and manganese). In otherwords, SiO refers to a colored material containing two or more of singlecrystal silicon, amorphous silicon, polycrystal silicon, Si₂O₃, Si₃O₄,Si₂O, and SiO₂. Thus, SiO can be distinguished from SiO_(x) (x is 2 ormore), which is clear and colorless or white. Note that in the casewhere a secondary battery is fabricated using SiO as a material thereofand the SiO is oxidized because of repeated charge and discharge cycles,SiO is changed into SiO₂ in some cases.

Alternatively, for the negative electrode active material, an oxide suchas titanium dioxide (TiO₂), lithium titanium oxide (Li₄Ti₅O₁₂),lithium-graphite intercalation compound (Li_(x)C₆), niobium pentoxide(Nb₂O₅), tungsten oxide (WO₂), or molybdenum oxide (MoO₂) can be used.

Still alternatively, for the negative electrode active material,Li_(3−x)M_(x)N (M=Co, Ni, or Cu) with a Li₃N structure, which is anitride containing lithium and a transition metal, can be used. Forexample, Li_(2.6)Co_(0.4)N₃ is preferable because of high charge anddischarge capacity (900 mAh/g and 1890 mAh/cm³).

A nitride containing lithium and a transition metal is preferably used,in which case lithium ions are contained in the negative electrodeactive material and thus the negative electrode active material can beused in combination with a material for a positive electrode activematerial which does not contain lithium ions, such as V₂O₅ or Cr₃O₈. Inthe case of using a material containing lithium ions as a positiveelectrode active material, the nitride containing lithium and atransition metal can be used for the negative electrode active materialby extracting the lithium ions contained in the positive electrodeactive material in advance.

Alternatively, a material which causes a conversion reaction can be usedfor the negative electrode active material; for example, a transitionmetal oxide which does not cause an alloy reaction with lithium, such ascobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may beused. Other examples of the material which causes a conversion reactioninclude oxides such as Fe₂O₃, CuO, Cu₂O, RuO₂, and Cr₂O₃, sulfides suchas CoS_(0.89), NiS, and CuS, nitrides such as Zn₃N₂, Cu₃N, and Ge₃N₄,phosphides such as NiP₂, FeP₂, and CoP₃, and fluorides such as FeF₃ andBiF₃. Note that any of the fluorides can be used as a positive electrodeactive material because of its high potential.

The negative electrode active material layer 205 may further include abinder for increasing adhesion of active materials, a conductiveadditive for increasing the conductivity of the negative electrodeactive material layer 205, and the like in addition to theabove-described negative electrode active materials.

As an electrolyte in the electrolytic solution 210, a material whichcontains lithium ions serving as carrier ions is used. Typical examplesof the electrolyte are lithium salts such as LiPF₆, LiClO₄, Li(FSO₂)₂N,LiAsF₆, LiBF₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, and Li(C₂F₅SO₂)₂N. One of theseelectrolytes may be used alone, or two or more of them may be used in anappropriate combination and in an appropriate ratio. In order tostabilize a reaction product, a small amount (1 wt %) of vinylenecarbonate (VC) may be added to the electrolytic solution so that thedecomposition amount of the electrolytic solution is further reduced.

As a solvent of the electrolytic solution 210, a material in whichcarrier ions can transfer is used. As the solvent of the electrolyticsolution, an aprotic organic solvent is preferably used. Typicalexamples of aprotic organic solvents include ethylene carbonate (EC),propylene carbonate, dimethyl carbonate, diethyl carbonate (DEC),γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, and thelike, and one or more of these materials can be used. When a gelledhigh-molecular material is used as the solvent of the electrolyticsolution, safety against liquid leakage and the like is improved.Furthermore, the secondary battery can be thinner and more lightweight.Typical examples of gelled high-molecular materials include a siliconegel, an acrylic gel, an acrylonitrile gel, polyethylene oxide,polypropylene oxide, a fluorine-based polymer, and the like.Alternatively, the use of one or more of ionic liquids (room temperaturemolten salts) which have features of non-flammability and non-volatilityas a solvent of the electrolytic solution can prevent the secondarybattery from exploding or catching fire even when the secondary batteryinternally shorts out or the internal temperature increases owing toovercharging and others.

As the separator 207, an insulator such as cellulose (paper),polyethylene with pores, and polypropylene with pores can be used.

FIG. 2B illustrates an example in which the number of electrode layersis two (two layers of the positive electrode 203 and the negativeelectrode 206). In order that the area (size) of the secondary batteryis decreased without change in capacity of the secondary battery, thesecondary battery can be downsized by increasing the number of electrodelayers to more than two. However, if the number of electrode layersexceeds 40, the secondary battery has a large thickness and might loseits flexibility. Therefore, the number of electrode layers is set to 40or less, preferably 20 or less. In the case of double-sided coating bywhich both sides of the positive electrode current collector are coatedwith the positive electrode active material layer 202, or in the case ofdouble-sided coating by which both sides of the negative electrodecurrent collector 204 are coated with the negative electrode activematerial layer 205, the number of electrode layers can be decreased to10 or less without change in capacity of the secondary battery.

The stacked layer including the sheet-like positive electrode 203, theseparator 207, and the sheet-like negative electrode 206 is sealed byheat sealing.

In the secondary battery, a thin flexible film (such as a laminate film)is used as an exterior body. The laminate film refers to a stacked filmof a base film and an adhesive synthetic resin film, or a stacked filmof two or more kinds of films. For the base film, polyester such as PETor PBT, polyamide such as nylon 6 or nylon 66, an inorganic film formedby evaporation, or paper may be used. For the adhesive synthetic resinfilm, polyolefin such as PE or PP, an acrylic-based synthetic resin, anepoxy-based synthetic resin, or the like may be used. An object islaminated with the laminate film by thermocompression bonding using alaminating apparatus. Note that an anchor coat agent is preferablyapplied as pretreatment for the laminating step so that the adhesionbetween the laminate film and the object can be increased. As the anchorcoat agent, an isocyanate-based material or the like may be used.

In this specification, heat sealing refers to sealing bythermocompression bonding, and means that an adhesive layer partlycovering the base film or an outermost or innermost layer with a lowmelting point in the laminate film is melted by heat and attached bypressure.

The positive electrode current collector 201 and the negative electrodecurrent collector 204 also serve as terminals for electrical contactwith the outside. For this reason, the positive electrode currentcollector 201 and the negative electrode current collector 204 areprovided so that part of the positive electrode current collector 201and part of the negative electrode current collector 204 are exposedoutside a film 208 and an exterior body 209 as illustrated in FIG. 2A.In the case where a larger number of electrode layers are stacked, aplurality of positive electrode current collectors 201 are electricallyconnected by ultrasonic welding, and a plurality of negative electrodecurrent collectors 204 are electrically connected by ultrasonic welding.Note that in FIG. 2B, part of the negative electrode current collector204 extends to the outside beyond the exterior body 209.

The laminated secondary battery obtained as described above is firstattached to the region with a large radius of curvature of the supportstructure body 101 and then to the other region. By first attaching thesecondary battery to the region with a large radius of curvature, damageto the secondary battery can be reduced during attachment to the supportstructure body 101.

Although FIG. 2A illustrates the example of sealing with the film 208and the exterior body 209, the present invention is not particularlylimited to this example, and a single film folded in half may be used asan exterior body. An example different from that in FIGS. 2A and 2B isillustrated in FIGS. 10A to 10F. A film 11 is folded in half so that twoend portions overlap, and is sealed on three sides with an adhesivelayer. A manufacturing method in this example is described below withreference to FIGS. 10A to 10F.

First, the film 11 is folded in half as illustrated in FIG. 10A. Inaddition, a positive electrode current collector 12, a separator 13, anda negative electrode current collector 14 which are components of asecondary battery and stacked as illustrated in FIG. 10B are prepared.Furthermore, two lead electrodes 16 with sealing layers 15 illustratedin FIG. 10C are prepared. The lead electrodes 16 are each also referredto as a lead terminal and provided in order to lead a positive electrodeor a negative electrode of a secondary battery to the outside of anexterior film. Then, one of the lead electrodes is electricallyconnected to a protruding portion of the positive electrode currentcollector 12 by ultrasonic welding or the like. Aluminum is used as amaterial of the lead electrode connected to the protruding portion ofthe positive electrode current collector 12. The other lead electrode iselectrically connected to a protruding portion of the negative electrodecurrent collector 14 by ultrasonic welding or the like. Nickel-platedcopper is used as a material of the lead electrode connected to theprotruding portion of the negative electrode current collector 14. Then,two sides of the film 11 are sealed by thermocompression bonding, andone side is left open for introduction of an electrolytic solution. Inthermocompression bonding, the sealing layers 15 provided over the leadelectrodes are also melted, thereby fixing the lead electrodes and thefilm 11 to each other. After that, in a reduced-pressure atmosphere oran inert atmosphere, a desired amount of electrolytic solution isintroduced to the inside of the film 11 in the form of a bag. Lastly,the side of the film which has not been subjected to thermocompressionbonding and is left open is sealed by thermocompression bonding. In thismanner, a secondary battery 40 illustrated in FIG. 10D can bemanufactured. An edge region indicated by a dotted line in FIG. 10D is athermocompression-bonded region 17. An example of a cross-section takenalong a dashed-dotted line A-B in FIG. 10D is illustrated in FIG. 10E.As illustrated in FIG. 10E, the positive electrode current collector 12,a positive electrode active material layer 18, the separator 13, anegative electrode active material layer 19, and the negative electrodecurrent collector 14 are stacked in this order and placed inside thefolded film 11, an end portion is sealed with an adhesive layer 30, andthe other space is provided with an electrolytic solution 20.

Here, a current flow in charging a secondary battery will be describedwith reference to FIG. 10F. When a secondary battery using lithium isregarded as a closed circuit, lithium ions transfer and a current flowsin the same direction. Note that in the secondary battery using lithium,an anode and a cathode change places in charge and discharge, and anoxidation reaction and a reduction reaction occur on the correspondingsides; hence, an electrode with a high redox potential is called apositive electrode and an electrode with a low redox potential is calleda negative electrode. For this reason, in this specification, thepositive electrode is referred to as a “positive electrode” and thenegative electrode is referred to as a “negative electrode” in all thecases where charge is performed, discharge is performed, a reverse pulsecurrent is supplied, and a charging current is supplied. The use of theterms “anode” and “cathode” related to an oxidation reaction and areduction reaction might cause confusion because the anode and thecathode change places at the time of charging and discharging. Thus, theterms “anode” and “cathode” are not used in this specification. If theterm “anode” or “cathode” is used, it should be mentioned that the anodeor the cathode is which of the one at the time of charging or the one atthe time of discharging and corresponds to which of a positive electrodeor a negative electrode.

Two terminals in FIG. 10F are connected to a charger, and the secondarybattery 40 is charged. As the charge of the secondary battery 40proceeds, a potential difference between electrodes increases. Thepositive direction in FIG. 10F is the direction in which a current flowsfrom one terminal outside the secondary battery 40 to the positiveelectrode current collector 12, flows from the positive electrodecurrent collector 12 to the negative electrode current collector 14 inthe secondary battery 40, and flows from the negative electrode currentcollector 14 to the other terminal outside the secondary battery 40. Inother words, a current flows in the direction of a flow of a chargingcurrent.

Next, a display module to be attached to the secondary battery 103 isprepared. The display module refers to a display panel provided with atleast an FPC. The display module includes the display portion 102, anFPC 104, and a driver circuit and preferably further includes aconverter for power feeding from the secondary battery 103.

In the display module, the display portion 102 is flexible and a displayelement is provided over a flexible film. The secondary battery 103 andthe display portion 102 are preferably disposed so as to partly overlapwith each other. When the secondary battery 103 and the display portion102 are disposed so as to partly or entirely overlap with each other,the electrical path, i.e., the length of a wiring, from the secondarybattery 103 to the display portion can be shortened, whereby powerconsumption can be reduced.

Examples of methods for manufacturing the display element over theflexible film include a method in which the display element is directlyformed over the flexible film, a method in which a layer including thedisplay element is formed over a rigid substrate such as a glasssubstrate, the substrate is removed by etching, polishing, or the like,and then the layer including the display element and the flexible filmare attached to each other, a method in which a separation layer isprovided over a rigid substrate such as a glass substrate, a layerincluding the display element is formed thereover, the rigid substrateand the layer including the display element are separated from eachother using the separation layer, and then the layer including thedisplay element and the flexible film are attached to each other, andthe like.

In this embodiment, a manufacturing method which allows heat treatmentto be performed at 400° C. or higher and which can improve thereliability of the display element, i.e., a technique in which aseparation layer is provided over a rigid substrate such as a glasssubstrate as disclosed in Japanese Published Patent Application No.2003-174153, is used so that the display portion 102 can be anactive-matrix display device capable of displaying high-resolutionimages.

The technique disclosed in Japanese Published Patent Application No.2003-174153 enables transistors including polysilicon in active layersor transistors including oxide semiconductor layers to be provided overa flexible substrate or film. These transistors are used as switchingelements, and electroluminescent (EL) elements are provided.

In a common structure of the EL element, a layer including alight-emitting organic compound or inorganic compound (hereinafterreferred to as a light-emitting layer) is provided between a pair ofelectrodes, and when a voltage is applied to the element, electrons andholes are each injected and transported from the pair of electrodes tothe light-emitting layer. When those carriers (electrons and holes)recombine, an excited state of the light-emitting organic compound orinorganic compound is formed, and when the light-emitting organiccompound or inorganic compound returns to a ground state, light isemitted.

Further, kinds of excited state that can be formed by an organiccompound are a singlet excited state and a triplet excited state. Lightemission in the case of a singlet excited state is referred to asfluorescence, and light emission in the case of a triplet excited stateis referred to as phosphorescence.

Such a light-emitting element is usually formed of thin films which havean approximate thickness of submicrons to several microns. Therefore,they can be manufactured to be thin and light, which is a largeadvantage. Further, such light-emitting elements also have an advantagein that the period of time from when the carriers are injected untillight is emitted is microseconds at the most, so they have a very highresponse speed. Moreover, because sufficient light emission can beobtained with a direct current voltage of approximately several toseveral tens of volts, power consumption is also relatively low.

EL elements have a wider viewing angle than that of liquid crystalelements and are preferable as display elements in the display portion102 when a display region has a curved surface. In addition, EL elementsare preferable as display elements in the display portion 102 in thatunlike liquid crystal elements, EL elements do not require a backlight,which makes it possible to reduce power consumption, the number ofcomponents, and the total thickness.

Note that methods for manufacturing display elements over a flexiblefilm are not limited to the method mentioned above (Japanese PublishedPatent Application No. 2003-174153). Methods and materials formanufacturing EL elements may be known methods and materials and aretherefore not described here.

The display device used as the display portion 102 may only be capableof simply displaying single-color images or displaying numbers.Therefore, a passive-matrix display device may be used, in which case adisplay element may be manufactured over a flexible film using a methodother than the technique disclosed in Japanese Published PatentApplication No. 2003-174153.

The display module obtained by the above method is attached to thesecondary battery 103, and the secondary battery 103 and the displayportion 102 are electrically connected to each other, whereby theelectronic device 100 illustrated in FIG. 1B is completed. Furthermore,a metal cover, a plastic cover, or a rubber cover may be provided over aportion other than the display portion 102 to improve the appearance ofthe electronic device 100.

In the case where the electronic device 100 is provided with the displayportion, the screen size is not particularly limited as long as thedisplay portion is of such a size that it can be disposed over thesupport structure body. For example, in the case where the electronicdevice is worn on an arm, the maximum screen size is the product of anarm girth of 23 cm and a wrist-to-elbow length because the girth of anadult arm near a wrist is 18 cm±5 cm. The wrist-to-elbow length of anadult is shorter than or equal to a feet (30.48 cm); thus, the maximumscreen size of the display portion that can be disposed over the supportstructure body in the form of a cylinder tube in the electronic device100 that is worn on an arm is 23 cm×30.48 cm. Note that the screen sizehere does not refer to the size in a curved state but refers to the sizein a flat state. A plurality of display portions may be provided in oneelectronic device; for example, a second display portion smaller than afirst display portion may be included in an electronic device. Thedimension of the support structure body 101 is set larger than thescreen size of the display portion. In the case of using EL elements,when the display portion is of such a screen size that it can bedisposed over the support structure body, the sum of the weights of thedisplay panel and the FPC can be more than or equal to 1 g and less than10 g.

The thickness of the thinnest portion of the electronic device providedwith the display portion (the thickness of the support structure body101, the display portion 102, and the secondary battery 103 overlappingwith each other) can be less than or equal to 5 mm. The thickness of thethickest portion of the electronic device, which is a portion where thedisplay panel and the FPC are connected to each other, can be less than1 cm.

The total weight of the electronic device 100 can be less than 100 g.

The electronic device 100 can be put on an arm because part of thesupport structure body can be moved in the direction of the arrows 105illustrated in FIG. 1A. The electronic device 100 has a total weightless than 100 g, preferably less than or equal to 50 g and a smallmaximum thickness less than or equal to 1 cm; thus, a lightweightelectronic device can be provided.

The electronic device 100 has a plurality of curved surfaces withdifferent radii of curvature in a cross-section as illustrated in FIG.7A. FIG. 7A illustrates a center 700 of curvature and a center 701 ofcurvature.

Description is given of the radius of curvature of a surface withreference to FIGS. 9A to 9C. In FIG. 9A, on a plane 1701 along which acurved surface 1700 is cut, part of a curve 1702 is approximate to anarc of a circle, and the radius of the circle is referred to as a radius1703 of curvature and the center of the circle is referred to as acenter 1704 of curvature. FIG. 9B is a top view of the curved surface1700. FIG. 9C is a cross-sectional view of the curved surface 1700 takenalong the plane 1701. When a curved surface is cut along a plane, theradius of curvature of a curve depends on along which plane the curvedsurface is cut. Here, the radius of curvature of a curved surface isdefined as the radius of curvature of a curve on a plane along which thecurved surface is cut such that the curve has the smallest radius ofcurvature.

In the case of curving the electronic device 100 which has a lower armcontact surface (exposed back surface) of the exterior body on the innerside and a film surface (exposed front surface) of the display panel onthe outer side, a radius 1802 of curvature of an exterior body 1801(exposed back surface) on the side closer to a center 1800 of curvatureof the secondary battery and in contact with a support structure body1805 is smaller than a radius 1804 of curvature of a film 1803 on theside farther from the center 1800 of curvature (FIG. 8A). When theelectronic device 100 is curved and has an arc-shaped cross section,compressive stress is applied to the exposed back surface of theexterior body on the side closer to the center 1800 of curvature, andtensile stress is applied to the exposed surface of the film on the sidefarther from the center 1800 of curvature (FIG. 8B). The electronicdevice 100 can change its shape such that the exterior body 1801 on theside closer to the center of curvature has a curvature radius greaterthan or equal to 10 mm, preferably greater than or equal to 30 mm.

Note that the cross-sectional shape of the electronic device 100 is notlimited to a simple arc shape, and the cross-section of a portion incontact with a wrist can have an arc shape; for example, a shapeillustrated in FIG. 8C or the like can be used. When the curved surfaceof the secondary battery has a shape with a plurality of centers ofcurvature, the electronic device 100 can change its shape such that acurved surface with the smallest radius of curvature among radii ofcurvature with respect to the plurality of centers of curvature, whichis a surface of the exterior body 1801 on the side closer to the centerof curvature, has a curvature radius greater than or equal to 10 mm,preferably greater than or equal to 30 mm.

FIG. 7B illustrates a bottom view of the electronic device 100 which isseen from the exposed back surface side of the support structure body.FIG. 7C illustrates a side view of the electronic device 100.

Embodiment 2

In this embodiment, an example of a method for charging a secondarybattery using an antenna is described.

Since an electronic device is to be in contact with part of a humanbody, it is preferable for safety that input and output terminals forcharging or discharging a secondary battery be not exposed. In the casewhere the input and output terminals are exposed, the input and outputterminals might short-circuit by water such as rain, or the input andoutput terminals might be in contact with a human body and cause anelectric shock. The use of an antenna enables a structure in which theinput and output terminals are not exposed on a surface of theelectronic device.

Note that this embodiment is the same as Embodiment 1 except that anantenna and an RF power feed converter are provided; therefore, theother components are not described in detail here.

In accordance with Embodiment 1, a flexible secondary battery is fixedto a support structure body, and a display module is attached to thesecondary battery. An RF power feed converter and an antenna which areelectrically connected to the secondary battery are provided. The RFpower feed converter is fixed so as to overlap with part of a displayportion.

The RF power feed converter and the antenna weigh less than or equal to10 g, and the total weight does not significantly differ from that inEmbodiment 1.

FIG. 3 illustrates a schematic diagram of an electronic device 300including an antenna (not illustrated) and a charger 301. When theelectronic device 300 is disposed over the charger 301, electric powercan be supplied from an antenna of the charger 301 to the electronicdevice 300 to charge a secondary battery of the electronic device 300.

Information such as the remaining amount or time to full charge can bedisplayed on a display portion of the electronic device 300.

This embodiment can be freely combined with Embodiment 1.

Embodiment 3

In this embodiment, an example of a structure for preventing theformation of wrinkles or the leakage of an electrolytic solution whichmight occur when a secondary battery is curved is described withreference to FIGS. 4A and 4B.

In Embodiment 1, the secondary battery is sealed with the laminate film,and the periphery is fixed in one portion (in the cross-sectional view).Thus, if the sealing is broken at any place when the secondary batteryis bent repeatedly or subjected to impact, the electrolytic solutionleaks from the inside. In the case where the laminate film is fixed inone portion, bending stress due to repeated bending of or impact on thesecondary battery is concentrated in that portion, whereby the sealingcannot be maintained.

In view of this, in this embodiment, two films are fixed in two portionsas illustrated in FIG. 4A. FIG. 4A illustrates a schematiccross-sectional view of a secondary battery 400 whose positive andnegative electrodes are sealed with two films. By fixing in twoportions, bending stress is relaxed and the sealing can be maintained.

A structural example different from that in Embodiment 1 is illustratedin FIG. 4B.

FIG. 4B illustrates an example in which a display portion 402 isprovided on the front surface side of a support structure body 401 andthe secondary battery 400 is disposed on the back surface side.

In FIG. 4B, the support structure body 401 is provided with an opening,and an FPC 403 extending from the display portion 402 and an FPC 404extending from the secondary battery are electrically connected to eachother through the opening.

In this embodiment, the size of the opening provided in the supportstructure body 401 is not particularly limited, and as long as a certaindegree of mechanical strength can be secured, the area of the openingmay be larger than that of the display portion 402, and the displayportion may be set in the opening. In that case, the secondary battery400 and the display portion 402 may be in contact with each other. Asthe size of the opening increases, the weight of the support structurebody decreases. Thus, the total weight can be decreased.

This embodiment can be freely combined with Embodiment 1.

Example 1

FIG. 5 is a photograph of an electronic device which is manufactured inaccordance with Embodiment 1 and is worn on an arm with an imagedisplayed on a display portion.

The electronic device shown in FIG. 5 is 77 mm long, 60 mm wide, and 57mm high, and the dimension is determined by a stainless steel supportstructure body. A display panel has an external size of 51.5 mm×92.15mm, and the display region has a size of 42.12 mm×74.88 mm. Theelectronic device has a total weight of 40 g to 50 g, and the sum of theweights of the display panel and an FPC can be approximately 2 g. Notethat the term “FPC” in this specification refers to a flexible printedwiring board, in which a plurality of metal foil (e.g., Cu, Ni, or Au)patterns are formed over a base member of a polyimide resin, an epoxyresin, or the like. An anisotropic conductive film (ACF) used forcompression bonding is formed along a side of an end of the FPC so as tocross end portions of the plurality of arranged metal foil patterns. Anexternal connection terminal of the display panel and the FPC areelectrically connected to each other by compression bonding using theACF provided over the FPC.

As a secondary battery, a laminated secondary battery is used, and as apositive electrode active material, lithium iron phosphate (LiFePO₄) isused. Lithium iron phosphate can improve the safety of the secondarybattery.

FIG. 6 is a schematic cross-sectional view of the secondary battery. Inthis secondary battery, sheet-like positive electrode current collectors601, sheet-like positive electrode active material layers 602,separators 607, negative electrode current collectors 604, and negativeelectrode active material layers 605 are stacked, the other region isfilled with an electrolytic solution 610, and these components areenclosed by a film 608 and an exterior body 609 made of a film with adepressed portion.

As illustrated in FIG. 6, the number of electrode layers is 16. Thestructure shown in FIG. 6 includes eight layers of negative currentcollectors 604 and eight layers of positive electrode current collectors601, i.e., 16 layers in total. Note that in a cross-section of anegative electrode extraction portion illustrated in FIG. 6, the eightlayers of negative electrode current collectors 604 are bonded byultrasonic welding.

The thickness of the thinnest portion of the electronic device providedwith the display portion (the thickness of the support structure body,the display portion, and the secondary battery overlapping with eachother) is 3.2 mm. The thickness of the thickest portion of theelectronic device, which is a portion where the display panel and theFPC are connected (a region where an external connection terminal isprovided), is 6 mm. Note that an IC chip, a passive electroniccomponent, or the like may be directly attached to the FPC. However, inthat case, the IC chip or the like is not regarded as part of the FPC.In the case where a passive electronic component such as an L, C, or Rcomponent, a driver circuit IC chip, a CPU, a memory, or the like isdirectly attached to the FPC, that portion may be the thickest portionof the electronic device.

In this example, lithium iron phosphate is used as the positiveelectrode active material. By appropriately changing, for example, thepositive electrode active material or the negative electrode activematerial so as to increase the volume energy density of the secondarybattery, further reductions in size and weight can be achieved. Forexample, when lithium cobalt oxide (LiCoO₂) is used as the positiveelectrode active material, the volume energy density is increased. Thus,when a secondary battery having the same capacity as that of thisexample is fabricated using lithium cobalt oxide, the secondary batterycan be thinner and lighter.

Electric power for displaying the image shown in FIG. 5 is supplied onlyfrom the secondary battery overlapping with the display portion.

As a matter of course, the image displayed on the display portion inFIG. 5 is not processed and is the one actually displayed in full color.The resolution of the display portion in FIG. 5 is 326 ppi. Each pixelincludes three transistors, and an oxide semiconductor (InGaO₃(ZnO)_(m))is used in the transistors. Connection terminals for charging and forvideo signal inputting are provided in an end portion of the supportstructure body and are connected to an external charging device or anexternal driving device when the electronic device is not in use by auser, i.e., at the time of charging or video signal inputting. When theelectronic device is in use by a user, i.e., worn on an arm with animage displayed, a cord such as a wiring is not connected to an externaldriving device.

The electronic device shown in FIG. 5 has a total weight of 50 g or lessand is light when worn on an arm. In addition, the electronic devicepresents an appearance with an attractive design and can thus be used asan accessory.

EXPLANATION OF REFERENCE

100: electronic device, 101: support structure body, 102: displayportion, 103: secondary battery, 104: FPC, 105: arrow, 201: positiveelectrode current collector, 202: positive electrode active materiallayer, 203: positive electrode, 204: negative electrode currentcollector, 205: negative electrode active material layer, 206: negativeelectrode, 207: separator, 208: film, 209: exterior body, 210:electrolytic solution, 300: electronic device, 301: charger, 400:secondary battery, 401: support structure body, 402: display portion,403: FPC, 404: FPC, 601: positive electrode current collector, 602:positive electrode active material layer, 604: negative electrodecurrent collector, 605: negative electrode active material layer, 607:separator, 608: film, 609: exterior body, and 610: electrolyticsolution.

This application is based on Japanese Patent Application serial no.2013-147187 filed with Japan Patent Office on Jul. 16, 2013, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. An arm-worn electronic device comprising: astructure body comprising a curved portion, the structure body beingconfigured to be worn on a user's arm; a display portion placed on oneof surfaces of the structure body opposite to the user's arm when thestructure body is worn on the user's arm; and a secondary battery placedbetween the user's arm and the other of the surfaces of the structurebody on a side of the user's arm when the structure body is worn on theuser's arm, wherein the secondary battery is placed on the curvedportion, wherein the display portion is placed on the curved portion,wherein the secondary battery comprises a region overlapping the displayportion with the structure body provided therebetween.
 2. An arm-wornelectronic device comprising: a structure body comprising a curvedportion, the structure body being configured to be worn on a user's arm;a display portion placed on one of surfaces of the structure bodyopposite to the user's arm when the structure body is worn on the user'sarm; and a secondary battery placed between the user's arm and the otherof the surfaces of the structure body on a side of the user's arm whenthe structure body is worn on the user's arm, wherein the secondarybattery is placed on the curved portion, wherein the display portion isplaced on the curved portion, wherein the secondary battery comprises aregion overlapping the display portion with the structure body providedtherebetween, wherein the secondary battery is sealed using a film,wherein two end portions of the film overlap each other by folding thefilm, wherein one side among four sides of the film comprises a foldedportion, and wherein the other three sides of the film has an adhesivelayer.
 3. The arm-worn electronic device according to claim 1, whereinthe secondary battery comprises a lead electrode, wherein one of theother three sides comprises an edge placing the lead electrode, andwherein the adhesive layer is between the lead electrode and the film.